1. Field of the Invention
The present invention relates to a visual magnetic recording medium capable of having produced thereon permanent but erasable visual recordings of various kinds of information, and a method of making such visual magnetic recording medium.
2. Prior Art
There have been proposed three types of recording mediums which are capable of having produced thereon a visual image of magnetically recorded information.
The first type of known recording medium comprises a magnetic recording card such as disclosed in Japanese Patent Publication (JP-B) No. 56-852. The disclosed magnetic card is composed of a magnetic recording layer, a base member of sheet material having an aperture or window therein, and a transparent sheet, these components being united one above another with the window sealingly and floatingly retaining therein fine magnetic particles. The fine magnetic particles are caused to be moved under the action of a magnetic field when selected areas of the magnetic recording layer are magnetized, thereby producing traces or images of recorded information which can be observed through the transparent sheet.
The second type of known recording medium is disclosed in Japanese Patent Publication (JP-B) No. 60-27003, in which a multiplicity of microcapsules each containing a liquid and magnetic particles (flakes) suspended in the liquid and a coloring material are coated over the front surface of a base member by means of a transparent binder, the base having a selected color. The magnetic flakes are changed in posture under the action of a proximal magnetic field in such a manner that when the flakes are oriented substantially parallel to the display surface, the color of the coloring material is observed in preference to the color of the base member, whereas when the flakes are oriented substantially perpendicular to the display surface, the color of the base member is observed in preference to the color of the coloring material.
The third type of known recording medium, as shown in Japanese Patent Publication (JP-B) No. 48-41221, includes a coating of microcapsules provided over one surface of a base member, the microcapsules containing tiny droplets of fluid, and highly reflective, magnetic flake-like particles suspended in the fluid. The magnetic flake-like particles are selectively oriented between a first position in which incident light rays striking the surface of the recording medium are reflected by the highly reflective, magnetic flake-like particles in a direction away from the base member, and a second position in which the incident light rays are scattered by the highly reflective, magnetic flake-like particles into the microcapsules and absorbed there. As a consequence, a visual contrast is created between an area in which the magnetic flake-like particles assume the first position, and an area in which the magnetic flake-like particles are disposed in the second position.
The first-mentioned recording medium or card is advantageous for its superior retentivity or memory of recorded information. This recording card however has a drawback in that due to the presence of the window in which the fine magnetic particles are contained, the window portion of the recording card is structurally weaker than the remaining portion. Accordingly, the recording card tends to be bent or folded over about the window portion. When subjected to undue or repeated bending forces, the recording card of a three-ply construction is likely to cause an interlamilar separation in the vicinity of the window portion or cause a permanent deformation on a portion of the magnetic recording layer which corresponds in position to the window portion. The magnetic card thus damaged cannot be used any more.
The second and third types of recording mediums do not have any window or opening and hence they are resistant to bending forces or stresses. However, these recording mediums have not been distributed to the market as they only have an information retentivity which is substantially lower than practically required. The reasons for such insufficient information retentivity are as follows.
In the recording mediums, the magnetic flake-like particles are preoriented parallel to the plane of the recording medium. When information is to be recorded, the recording medium is subjected to a recording magnetic field applied perpendicular to the plane of the recording medium. Those magnetic flake-like particles exposed to the magnetic field are reoriented substantially perpendicular to or at an angle to the plane of the recording medium while the flake-like particles not exposed to the magnetic field remain in their preoriented position parallel to the plane of the recording medium. As a result, a contrast is created due to the difference in reflectivity between the exposed flake-like particles and the unexposed flake-like particles, or due to scattering of the incident light rays by the exposed flake-like particles and reflection of the incident light rays by the unexposed flake-like particles.
The recorded information is retained for a long period of time even after the recording medium is separated from the recording magnetic field so long as the recording medium has a remnant magnetic force large enough to produce a local magnetic field which acts on the flake-like particles. As described above, the magnetic flake-like particles are preoriented in a position parallel to the plane of the recording medium for normally reflecting the incident light rays. Therefore, a magnetic field applied for the preorientation of the flake-like particles must have a certain strength. The preoriented flake-like particles are moved from the horizontal position into a tilted or substantially erect position for scattering the incident light rays when subjected to the recording magnetic field. When the recording magnetic field is removed, the individual flake-like particles each constitute a permanent magnet having north and south poles at opposite ends and are displaced relative to one another through repulsion and attraction between adjacent magnetized flake-like particles until the magnetic potential between all adjacent flake-like particles becomes minimal. The flake-like particles are thus aligned with lines of magnetic flux and retained in this aligned position against relative displacement, thus retaining or memorizing the recorded information. The relative displacement of the flake-like particles is achieved mainly under the action of the recording magnetic field, however, the flake-like particles as they are displaced concurrently receive a substantial influence of a remnant magnetic force produced by the preorienting magnetic field. The remnant magnetic force of the preorienting magnetic field interferes with a remnant magnetic force produced by the recording magnetic field. With this magnetic interference, the magnetism of the flake-like particles acting as permanent magnets is deteriorated for a relatively short period of time, thus lowering the information retentivity of the recording medium.
Furthermore, the recording mediums are likely to be stacked for storage or while in use in which instance the remnant magnetic force of one recording medium may exert a substantial influence upon flake-like particles in an adjacent recording medium, thereby lowering the information retentivity of the recording medium.